Upcycling of Spent Lithium Cobalt Oxide Cathode from Discarded

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Upcycling of Spent Lithium Cobalt Oxide Cathode from Discarded Lithium-ion Batteries as a Solid Lubricant Additive Vihang Parimal Parikh, Arman Ahmadi, Mihit H Parekh, Farshid Sadeghi, and Vilas G. Pol Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.8b07016 • Publication Date (Web): 01 Mar 2019 Downloaded from http://pubs.acs.org on March 5, 2019

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Environmental Science & Technology

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Upcycling of Spent Lithium Cobalt Oxide Cathode

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from Discarded Lithium-ion Batteries as a Solid

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Lubricant Additive

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Vihang P. Parikh1, Arman Ahmadi2, Mihit H. Parekh1, Farshid Sadeghi2,*, Vilas G. Pol1,*

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1Davidson

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2School

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KEYWORDS: Lithium cobalt oxide, Solid lubricant, Graphene, Wear, Coefficient of friction

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ABSTRACT

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This manuscript provides an alternative solution to overgrowing battery recycling via upcycling

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of spent lithium cobalt oxide (LCO) as a new promising solid lubricant additive. The advanced

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solid lubricant mixture of graphene, Aremco binder and recycled LCO formulated a spray with the

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use of excess volatile organic solvent. Numerous flat steel disks were spray coated with new

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lubricant formulation and naturally dried followed by curing at 180°C. When tested on a ball-on-

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disk up to 230 m distance, the composite new solid lubricant reduces coefficient of friction (COF)

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by 85% between two steel surfaces compare to unlubricated surfaces under constant 1 GPa

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Hertzian pressure in an ambient environment. Tribofilm composition, particle size and type of

School of Chemical Engineering, Purdue University, West Lafayette, IN 47907, USA

of Mechanical Engineering, Purdue University, West Lafayette, IN 47907, USA

ACS Paragon Plus Environment

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contact are identified as an important parameters to improve COF. Scanning electron microscopy

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studied the morphology and energy dispersive X-ray spectroscopy analyzed the composition of

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pristine and tested tribofilm. Upcycled spent low value LCO powder is used as lubricant additive

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in tribology for the first time with exceptional lubricious properties.

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INTRODUCTION

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In the early 1980s, lithium cobalt oxide (LiCoO2, LCO) was first reported by Dr. John

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Goodenough as a suitable cathode1 material in the lithium-ion battery (LIB). From its

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implementation in commercial lithium ion battery (by Sony Inc. in 1991), it has been extensively

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used until today and most successful due to high specific capacity2 and better cycle performance,

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while maintaining high operating voltage. In LCO crystal structure, cobalt and lithium occupy

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octahedral sites3 in the alternate layer forming hexagonal symmetry. When potential is applied,

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lithium ions splits from LCO, diffuses through the electrolyte, meets electrons travelled from outer

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circuit and intercalate as Li in the graphitic anode forming LiC6 structure. During battery discharge

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Li ions splits from LiC6 structure, Li ions migrates back to cathode and electrons are released for

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utilization.

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As the demand for LIBs is rapidly increasing due to various electronic applications and the

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emerging trend of electric cars, the waste generated after its useful life is also increasing. As of

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today, only 5% LIBs are recycled in the USA and the rest becomes landfill waste.4 To address this

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issue, recycling of LIBs seems a reasonable solution and several recycling methods have been

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reported in the literature. Many efforts demonstrated ways to recycle cathode after opening the

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used batteries. Zhang5,6 X. et al. showed that trichloroacetic acid (TCA) and trifluoroacetic acid

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(TFA) along with hydrogen peroxide reductant can leach lithium and cobalt up to 90%. Yao L. et


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al. used D,L malic acid7 as a leaching agent as well as chelating agent to recycle

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LiNi1/3Co1/3Mn1/3O2 (LNCMO, different type of cathode material). Santana I. L. et al. used citric

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acid8 as a leaching agent with enhanced recovery. To achieve higher metal recovery, Jie G. et al

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used iron powder9 to reduce LCO first followed by acid leaching, which eliminated the use of

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peroxide. Furthermore, they enhanced the yield of valuable metals by optimizing the ball milling

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parameters10. As shown by Yaoguang G. et al in the case of indium recovery, computational

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thermodynamic11 approach provided insights to improve acid leaching process. Though these

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methods show fascinating results, it is very difficult to implement such ideas commercially,

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especially due to the high cost of leaching agents, waste generated and purification after use.

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Additionally, the secondary product i.e. recovered LCO requires enrichment of lithium to achieve

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comparable battery performance of pristine LCO. It is also known that LCO can act as a

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photocatalyst8 to split water into hydrogen and oxygen or digest organic dye. In past, our research

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team developed upcycling12,13,14 approach to convert low value waste plastics to high value

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carbonaceous materials. Upcycled plastic derived solid, dense, carbon spheres were used as an

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lithium ion battery anode2 and lubrication additive15 in standard oils. This motivated us to find an

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alternative application of LCO obtained from waste batteries in tribology field. In this study, for

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the first time it is shown that LCO can be utilized as a component of lubrication tribofilm with

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graphene-based solid lubricant.

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The main function of the lubricant is to reduce the coefficient of friction between two mechanical

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parts in contact when they are in relative motion.16 This leads to an improvement in the efficiency

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and life of the components.17 Lubricants are usually in the form of liquids (e.g. oils), gels (e.g.

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grease) or solids (e.g. graphite). Contrary to grease or oil fluid films for hydrodynamic lubrication,

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solids can be additives in oils, greases, high-performance anti-friction coatings and anti-seize


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pastes.18 Solid particles fill in the micro valleys and peaks on apparent smooth surface with

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adherence to the surface and coherence between the particles, while maintaining uniform thickness

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irrespective of speed, temperature, and load.16

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Solid lubricants are increasingly being applied to the various sliding parts in different

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applications such as transportation, industrial, electric and electronics to reduce friction and wear.

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Tribological performance and surface adhesion of solid lubricant can be further improved with the

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help of metal / oxide additives with enhanced sliding properties. Such additives reported in the

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literature are molybdenum disulfide (MoS2), boron nitride (BN), polytetrafluoroethylene (PTFE)

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and graphene. MoS2 itself can be used as a solid lubricant as well as it can be an additive in other

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solid lubricants. Qiu M. et al. showed MoS2-graphite19 significantly improves friction coefficient.

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Haojie S. et al suggested that due to good dispersion stability20 and extremely thin laminated

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structure, MoS2/graphene oxide composites prevents contact between rough surfaces by filling

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micro-roughness. Similarly, Miyake and Wang showed that 4 nm carbon/boron nitride21 multilayer

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film gives the better coefficient of friction along with hardness. Pooley and Tabor reported PTFE22

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as low coefficient of friction (COF, value near to 0.2) thermoplastic and has been used extensively

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in various applications. However, LCO has not been suggested or reported as a solid lubricant

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additive in literature, which has layers of lithium and cobalt oxide. Individually, lithium containing

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materials has shown improvement in tribology. For example, Xiaoqiang F. et al. improved the

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tribological performance of bentone grease with the help of different lithium salts23 along with

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better load carrying capacity. There are many patents registered for wear resistive materials, which

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contains cobalt oxide.24–26 Cobalt oxide is found to be helpful in maintaining uniform film

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thickness with varying load.27 Assuming the lubricious properties of individual Li containing


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material and cobalt oxide, we proposed and tested LCO as a lubricating additive in presence of

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multilayer graphene and polymeric binder making a unique spray-able solid lubricant.

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In this work, LCO was recovered from a used industrial 18650 LIB (laptop battery) after

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complete discharge to use as a graphene-based solid lubricant additive. The discarded, discharged

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batteries were opened and obtained LCO material. This lubricant was prepared out of spent LCO,

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graphene nano-platelets and specific binder along with the excess of organic volatile solvent,

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which was applied on a steel plate for ball-on-disk configuration of tribology testing at the constant

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pressure of 1GPa. Also, three key parameters were explored to improve tribological performance.

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Scanning electron microscope (SEM) and energy dispersive X-ray spectrometry (EDX) analyses

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were conducted to identify and verify the compounds recovered from spent LIBs.

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Materials and Methods

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As shown in Figure 1a, schematic shows a typical laptop battery comprising eight 18650 cells

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(18 mm diameter, 65 mm height, cylindrical) arranged as 2 parallel column, each having 4 cells in

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series resulting in 15.6 V with 5200 mAh capacity. Upon reverse calculation, each 18650 cell

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should have 3.9 V and 1300 mAh capacity. These values were in accordance with actual

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measurements. Before these cells were discharged, the measured current was 2.3 mA from each

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cell. To avoid the possibility of short-circuiting while opening in charged state that may lead to an

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explosion, every cell was first discharged at constant current of 35 mA for 48 hours. The

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discharging curve is shown in Figure 1b, which ensures the complete discharge as voltage reaches

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zero.

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To recover LCO, first outer stainless steel shell was cut from the circumference and

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longitudinally. Multiple layers of cathode (LCO on aluminum), anode (graphite on copper), and


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separator were bound in a cylindrical form which are clearly visible in Figure 1c. To maintain the

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mechanical strength of the layers and tight binding, a stainless steel rod is kept in the center of the

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cell. To avoid contamination each kind of layers were separated from each other before handling.

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LCO was firmly attached to both sides of current collecting aluminum foil. To avoid the use of

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acid, base or other organic/inorganic solvents, we used gentle ball milling to recover LCO from

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current collector, for which, cathode foils were cut into smaller pieces and ball milled for 10 min

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at 10 Hz using Quantachrome Ball Mill Instruments. To separate aluminum and LCO, assuming

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aluminum being malleable in contrast to LCO and it will stay among bigger particles while smaller

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particles will contain essentially LCO, we performed sieve separation using Quantachrome Tap

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Density machine. Upon requirement of further size reduction of LCO particles, we performed

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additional ball milling for 1 h at 15 Hz. Spray-able lubricant comprised of graphene, binder (which

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was a homogeneous mixture of half volume Aremco BondTM 570 and half volume acetone

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containing 22% solid particles by weight) and recycled LCO. To make the lubricant homogeneous,

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lubricant mixture was kept under constant stirring before coating. This method is portrayed as a

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pictorial form in Figure 1d. Spin coating led to non-uniform thickness of the solid lubricant due to

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large disc size and highly volatile organic solvent. To achieve uniform thickness and ease in

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handling, lubricant sprays (similar to commercial bottles) were prepared (Figure 1e). The bare,

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pristine, shiny metal plate used for coating is shown in Figure 1f. Prepared solution was sprayed

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and to control the thickness of coating, amount of acetone in excess was varied from 100 to 300%,

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which eventually evaporates during the curing process. To strengthen the bonds between substrate

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and coating, curing in the form of heating at 80°C for 20 minute followed by 180°C for 30 minute

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was provided (Figure 1g). Typical coating plate thickness observed for larger LCO particles was

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~120 micron and for finer particles was ~60 micron.


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Figure 1 a) A typical laptop battery module, b) discharge curve of an 18650 cell at 35 mA for 48 hours, c) disassembly of battery and separation of layers, d) lubricant preparation, e) LubeSpray bottle, which comprises LCO, Binder, graphene and solvent, f) flat disc used for coating, and g) spray coated disk for tribology testing


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To measure the friction coefficient of lubricant coated

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on metal disk, rotational sliding wear tests were

Experimental Parameters

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performed in the ball-on-disk configuration28 on a Bruker

Normal load

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UMT TriboLab™. A stationary 6.35 mm diameter 52100

Total displacement

175-230 m

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steel ball with the surface roughness of 50 nm and a

Frequency

0.9-1.5 Hz

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rotary 70 mm diameter 52100 steel coated disk were

Gas atmosphere

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used. Experimental parameters are presented in Table 1.

Temperature

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Prior to testing, all uncoated specimens were cleaned

Linear Velocity

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using acetone to remove residual debris on the surfaces.

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Each test was repeated at least three times with an error of measurement of wear and friction below

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5%.

Value 4N

Air 25°C 0.15 m/s

Table 1: Tribology Test Parameters

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Scanning electron microscope (SEM) imaging and energy dispersive X-ray (EDX) spectroscopy

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were carried out using a JEOL JCM-6000 Plus NeoScope Benchtop SEM. To examine the LCO

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powder at each stage, carbon tape with the sample on top was loaded inside the microscope

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chamber and then evacuated to a high vacuum. After optimization of the electron beam,

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micrographs of the sample were taken at different magnification. EDS analyses (JEOL Ltd.) were

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conducted to determine the relative proportions of elements, especially cobalt, carbon, aluminum,

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and fluorine. For further characterization of bonds in compounds, Thermo Scientific DXR2 Raman

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Microscope was used with 632 nm wavelength bulb as a source. Each spectra was captured with

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10 seconds exposure time at 10x magnification and 5 scans of the same spot.

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Results and Discussion

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SEM and EDS were performed on the cathode and recovered LCO to approximate the size of

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particles and identify compounds. Particle diameters ranging from 5-20 µm is observed on the


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surface of cathode. The presence of carbon, oxygen and cobalt is detected in EDS mapping (Figure

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2b-d). Raman spectra are also aligning with this observation. Peaks at 475 cm-1 and 588 cm-1 29,30

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(in Figure 3f, pristine LCO and recovered LCO spectra) are corresponding to LCO whereas 1332

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cm-1 and 1580 cm-1 30,31 (in Figure 3f, recovered LCO spectra) are D and G peaks corresponding

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to carbon. The small amount (

Upcycling of Spent Lithium Cobalt Oxide Cathode from Discarded

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